Japanese Patent Application Laid-Open Publication No. H7(1995)-74328 (Patent Document 1) describes a technique of directly bonding a first semiconductor substrate as an SOI layer and a second semiconductor substrate as a support substrate by firmly attaching them in a clean atmosphere. Forming a groove in an oxide film of the first semiconductor substrate as an SOI layer can reduce warpage of an SOI substrate.
Japanese Patent Application Laid-Open Publication No. 2000-31252 (Patent Document 2) describes a technique of detecting a thickness of a wafer rear-surface oxide film prior to treatment of the wafer, and applying a series of voltage sequence (detachment sequence) thereto according to the thickness. By application of the detachment sequence, a wafer detachment is smoothly performed.